The state of the conventional lighting fixtures used in commercial overhead lighting applications around the world, from the lighting fixtures or luminaires routinely mounted overhead in traditional office ceilings to the many types and shapes of fixtures used in outdoor street lighting, hasn't changed appreciably in a great many years. Standard lighting fixtures have remained typically large (24″×24″), thick (4″-10″), and weighty (7-30 lbs). The illumination they provide on surfaces below them is often brightest directly underneath, falling off in brightness quickly as distance from the fixture's location increases. Even though a given lighting application may require illumination held predominately to a limited geometric area (e.g. table top or work area), nearby viewers still receive unwanted glare when looking upwards at the fixture's physical aperture. While some conventional fixtures have been designed for limited-angle spotlighting purposes, they typically achieve net illumination efficiencies far lower than desired from a modern energy conservation perspective. Some light, is wasted by misdirection outside the area of interest, and other light, by the inefficiency the deliberate physical baffling added to block glare, which also adds significantly to the fixture's mechanical bulkiness.
A wide range of prior art has associated been with improvements in one aspect or another of the various lighting characteristics of this broad class of conventional lighting systems (e.g., fluorescent troffers and recessed quartz-halogen or metal halide down lighting cans). While modest gains have been made in luminaire efficiency, uniformity of illumination, and glare reduction, to mention a few, the lighting fixtures themselves have still remained as bulky and imposing as ever.
The net weight of conventional lighting fixtures is too heavy for most standard commercial ceiling frameworks without costly and cumbersome mechanical reinforcements. The heaviest lighting fixtures in most industrial applications need be suspended from the building's structural utility ceiling, rather than from its more convenient decorative one, unless the decorative one is reinforced substantially. Even in the case of the lightest weight conventional fixtures, reinforcing guide wires need be added to provide the extra mechanical support.
Conventional recessed lighting fixtures are also quite thick, which adds to the overhead plenum space required above the decorative ceiling to accommodate them, thereby reducing the effective ceiling height. Ceiling height reduction is particularly an issue in high-rise buildings where ceiling height is already limited by the building's structural boundary conditions.
Recently, commercial lighting fixtures utilizing assemblies of miniature light emitting diodes (LEDs) have started to appear in early applications featuring lighter more compact packaging. While this trend promises still greater lighting fixture advantages over time, early developments have yet to realize the full potential.
One reason the early LED lighting fixtures have lagged in achieving the compactness they promise is a consequence of their enormous brightness compared with that of the traditional light bulb alternatives. Light emitted by LEDs is created in very small geometric regions, and as a result, the associated brightness (i.e., lumens per square meter per solid angle in steradians) can be extremely hazardous to human view without additional packaging structures added to block, restrict or diffuse direct lines of view. One early solution to the LED's dangerous brightness levels has been to hide them from view in lighting fixtures, whose light is reflected indirectly upwards off wall and ceiling surfaces. While this approach prevents accidental view of the LED's directly, the associated fixtures are as bulky as conventional ones. Another solution involves diffusing the LED light over a larger output aperture. While this approach moderates aperture brightness in floodlighting applications, it does so at the expense of the fixture's thickness, and while also increasing the fixture's propensity for off-angle glare.
Looking at a bare LED emitter, even one combined with a reflector or a lens, is a quite unpleasant experience, typified by temporary blindness and a remnant image lasting minutes or longer. One of the most powerful of today's newest commercial LED emitters generates about 300 lumens in a 2.1 mm×2.1 mm emitting region. This is a brightness of 20 million Cd/m2 (nits). Such brightness appears more than 65,000 times as bright as the background brightness of the typical LCD display screens used in modern desktop computer monitors. Such brightness also appears to be 200 times brighter than the 18″ diameter aperture of commercial lighting fixtures using 250 W Hg arc lamps, which are already bright enough to cause viewers to see spots.
Modern LED light emitters require specialized lighting fixtures that capitalize on the LED's compactness potential, while providing a safe and desirable form of general illumination.
One of the more promising LED lighting adaptations involve a prior art LED illumination method, the so-called LED backlight. LED backlights are finding more frequent use as the source of rear illumination for the LCD screens used in large-format computer monitors and home televisions. The emerging LED backlights involved are about 1″-2″ thick and spread light from hundreds of internally hidden LED emitters uniformly over their screen area. By spreading and homogenizing the LED light emission, the LED backlight package thereby hides direct visibility of the otherwise dangerous brightness levels imposed by the bare LEDs themselves.
LED backlighting systems could be applied directly, for example, replacing the traditional 24″×24″×8″ fluorescent troffer in overhead office ceilings with significantly thinner and lighter weight alternatives.
As welcome as this possible LED lighting approach might be to commercial lighting use, the resulting fixture or luminaire is still a relatively thick and obtrusive one, veiling glare from its naturally wide angle emission remains an open issue, and beaming its output glow to limited task areas, is not provided. And while thinner than conventional light bulb based lighting fixture, LED backlights are still too thick to be conveniently embedded within the body of typical building materials such as ceiling tiles and wall board.
The light distributing engines of the present invention addresses all these needs by introducing a new class thin plate-like illumination systems (also, luminaires and lighting fixtures) whose square, rectangular and circular illuminating beams are distributed uniformly over enlarged output apertures of reduced brightness, while remaining sharply defined and well-directed in their illuminating extent from +/−5- to +/−60-degrees in each meridian, including all asymmetric combinations in between. Such light engines satisfy a wider range of general lighting services than any of the known alternatives, including wide area lighting, spot lighting, flood lighting, task lighting, and wall washing.
Semiconductor light emitting diodes (or LEDs) are chosen for all practical examples of the present invention because of their intrinsic compactness, because of their rapidly improving light generating capacity, and because of their increasingly low cost commercial availability. Over time, other suitable luminaire types may emerge based on organic LEDs (referred to as OLED), thin flat fluorescent sources, and flat micro plasma discharge sources, to mention a few.
While LEDs generally satisfy the present invention's need for thinness, applying LED light sources in accordance with the present invention involves a degree of adaptation for best mode usage. The present invention describes light distributing engines comprising commercial LED emitters with appropriate heat extraction means, associated optical couplers, associated light distributing optics, and when required, associated light spreading elements, all along with the low voltage DC power control electronics needed to achieve preferable sources of far-field illumination whose cross-sectional thickness is less than about 1-inch. Moreover, the new light distributing engine configurations safely dilute the LED's dangerously high brightness levels, without losing any of its other favorable lighting characteristics, such as tightly controlled beams of illumination and well-defined illumination patterns.
The light distributing engines of the present invention enable luminaires notably more compact in their physical size (approximately 2.5″×2.5″) and especially thin in their cross-section (approximately 5-10 mm). Though small in size, lumen outputs provided by these new light distributing engines range from hundreds of lumens per luminaire to thousands. And the resulting output illumination is constrained to beams organized as tightly as +/−5-degrees, as broadly as +/−60-degrees, or as any asymmetric combination in between—each with a sharp enough angular cutoff to reduce off-angle glare (i.e., veiling glare) along with the spatially-even square, rectangular and circular far-field illumination patterns sought by lighting architects and users alike.
Some best mode examples of practical applications incorporating the present thin illumination system inventions have been represented in U.S. Provisional Patent Application Ser. No. 61/104,606, Distributed Illumination System. Extended practical applications of the present invention in this reference involve more detailed system examples of the ease with which these thin illumination systems (also called luminaires and light distributing systems) may be incorporated within the physical body thickness of common building materials (as are used in forming commercial ceilings and walls), electrically interconnected, and electronically controlled (individually and as an interconnected distribution).